New rules proposed by the Environmental Protection Agency under the Safe Drinking Water Act are leading drinking water treatment professionals to re-evaluate present treatment capabilities and evaluate alternatives for the future. Depending on the size of the facility, water utilities using surface water as their source for drinking water will need to monitor a wider array of contaminants in the drinking water than heretofore. Monitoring results will lead to a determination as to whether enhanced surface water treatment is required to further protect end-users from microbial contaminants and disinfectant/disinfection by-products.
If higher-order drinking water treatment is needed, enhanced coagulation would be required. Chemical coagulants used in water treatment include inorganic coagulants and organic polymers. Inorganic coagulants include conventional metal salts (e.g. aluminum sulfate Al.sub.2 (SO.sub.4).sub.3 ; ferric chloride (FeCl.sub.3); lime (CaCO.sub.3) and polymerized metal salts (e.g. polyaluminum chloride p-AlCl.sub.3) or polyaluminum silicate sulfate (p-AlSiS).
However, higher doses of chemical coagulants have drawbacks as well. The benefits and proven efficacy of aluminum sulfate, the most widely used coagulant in drinking water treatment, is offset by the problem of residual metal contamination contributed by the metal salt and by performance problems at low temperatures. Higher doses of metal salts will generate large quantities of sludge and will depress pH, thereby requiting additional doses of pH adjustment chemicals. Use of synthetic organic polymer coagulants such as polyacrylamides and polyamines are also problematic since they may be toxic under certain circumstances.
These concerns have led to a ban on the use of many synthetic polymers in drinking water treatment in Germany, (Jackson, 1992, P. 1992. New Draft European Standards for Drinking Water Treatment Chemicals, paper delivered at the Intertech Conference: Flocculants, Coagulants and Precipitants for Drinking and Wastewater Treatment. Oct. 29-30, 1992. Herndon, Va.), in the Netherlands (Jackson, 1992, id.), and in Japan (Aizawa, T. et. al. 1990, Problems with Introducing Synthetic Polyelectrolyte Coagulants into the Water Purification Process, Water Supply Vol 8. Jonkoping, pp 27-35.). Elsewhere, doses of synthetic polymer coagulants are regulated to control potential problems with impurities (National Sanitation Foundation, 1988. Drinking Water Treatment Chemicals--Health Effects. Ann Arbor, Mich. ANSI/NSF60).
Attempts have been made to employ natural polymeric materials as coagulants in removal of greases, fats, and oils from industrial wastewater. Laurent (U.S. Pat. No. 5,269,939) describes a method for recovering suspended fats, oils, greases, proteins, and minerals from animal and/or food processing industrial wastewater streams using chitosan and clay. The wastewater freed of these materials is intended for discharge to municipal sewage treatment plants and the recovered solid material is a potential animal feed or fuel source. His method is "applicable to waste streams having any combination of fats, oils, greases, minerals, and/or proteins." (U.S. Pat. No. 5,269,939). There is a need to employ natural polymer coagulants and coagulant aids in other treatment contexts (i.e. drinking water treatment) in order to remove different sets of contaminants (i.e. particles, measured as turbidity or as number of particles; color; disinfectant/disinfection by-products).